The present invention relates to a fuel-feeding device of a variable venturi-type carburetor.
When starting an engine from a low temperature, a rich fuel mixture of an approximately 1:1 through 2:1 air-fuel ratio is necessary during the time the engine is rotated by the starter motor and an increased 8:1 through 10:1 air-fuel ratio is necessary after the engine begins to rotate by its own power. Toward this end, conventional carburetors have been constructed with the choke valve directly controlled by the vacuum produced in the intake passage located downstream of the throttle valve, so that the choke valve is opened when the engine begins to rotate by its own power and, accordingly, vacuum in the intake passage becomes great. However, in this case wherein the choke valve is directly controlled by vacuum produced in the intake passage, the opening of the choke valve occurs instantaneously when the engine begins to rotate by its own power. This along with the delay in response of the fuel-feeding operation temporarily results in an excessively lean air-fuel mixture fed into the cylinder of the engine. This in turn results in the problem of the engine stopping as soon as it begins to rotate on its own power.
To eliminate this problem, other conventional carburetors have been constructed to increase the amount of fuel fed into the cylinder of the engine when the engine begins to rotate by its own power so as to provide the optimum air-fuel ratio at that time. In such a case, however, the air-fuel mixture fed into the cylinder of the engine becomes excessively rich after the elapse of the delay in response of the fuel-feeding operation after the engine begins to rotate by its own power, causing the problem of misfires.